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A052812
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A simple grammar: power set of pairs of sequences.
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1
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1, 0, 1, 2, 3, 6, 9, 16, 24, 42, 63, 102, 157, 244, 373, 570, 858, 1290, 1930, 2858, 4228, 6208, 9084, 13216, 19175, 27666, 39804, 57020, 81412, 115820, 164264, 232178, 327220, 459796, 644232, 900214, 1254554, 1743896, 2418071, 3344896, 4616026
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| Number of partitions of n objects of two colors into distinct parts, where each part must contain at least one of each color. - Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Dec 28 2006
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LINKS
| INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 776
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FORMULA
| G.f.: exp(Sum((-1)^(j[1]+1)*(x^j[1])^2/(x^j[1]-1)^2/j[1], j[1]=1 .. infinity))
G.f.: Product_{k>=1} (1+x^k)^(k-1). - Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 17 2002
Weigh transform of b(n) = n-1. - Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Dec 28 2006
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MAPLE
| spec := [S, {B=Sequence(Z, 1 <= card), C=Prod(B, B), S= PowerSet(C)}, unlabeled]: seq(combstruct[count](spec, size=n), n=0..20);
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CROSSREFS
| Cf. A052847.
Sequence in context: A147227 A147063 A007865 * A062114 A094768 A093830
Adjacent sequences: A052809 A052810 A052811 * A052813 A052814 A052815
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KEYWORD
| easy,nonn
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AUTHOR
| encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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EXTENSIONS
| More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 17 2002
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